What is this?

So my neighbor is having her bathroom professionally remodelled. We have the same house, but just flipped. I went by yesterday and looked at the plumbing in her shower. What is the metal (for the shower) the is connected to the copper and is it necessary. It's also on the hand held part too.

There is no copper. Hmm, piping with cpvc wouldn't have been my first or second choice, but perhaps the house was originally plumbed with it. Yes, everything that is there is necessary, and apart from the rough-in mounting of the diverter and wall elbow, they seem to be doing a clean job of it.

This is all new plumbing. Although our houses are identical there were some marked differences in the plumbing. All my vents are PVC, wheras ALL their venting is copper. My stack was also PVC whereas their's cast iron.

That is just a temporary plug for testing purposes, BUT, you should NOT have capped off the extra port on the diverter. If it is not needed for a device, it should have been connected to one of the other outlet pipes.